BOSTON (CBS) — The Celtics’ bench is going to be missing a key contributor for the foreseeable future.

Forward Marcus Morris is expected to miss extended time due to an ongoing left knee issue, according to Yahoo! Sports’ Shams Charania. Morris told The Boston Herald’s Steve Bulpett that he could miss a couple of weeks with the injury, which has already caused Morris to miss 13 games so far this season.

Sources: Boston forward Marcus Morris is expected to miss extended time as he and the team work on solution for nagging left knee.

Marcus Morris told me he could miss a couple of weeks as he tries to get his left knee healthy. Waiting to speak with Stevens for further word. Guessing a plan won't be in place until he returns to Boston and is examined further Tuesday.

Morris missed the first two weeks of the regular season with the ailment and was sitting out the second half of back-to-backs after making his return. In his 16 games this season, Morris has averaged 12.1 points off of 41 percent shooting while averaging 5.5 rebounds per game.

In Morris’ absence, the Celtics will count on bigs like Aron Baynes, Daniel Theis and Semi Ojeleye to fill the void.